Additives Extraction from polymers

In SEC analysis of additive extracts from polymers, the effect of the extraction solvent on the mobile phase is less critical than in HPLC analysis. The extraction solvents typically employed generally do not interfere with the SEC mobile phases. Moreover, the same solvents are often used both as extraction solvent and as mobile phase. Therefore, there is no need to evaporate the extract to dryness prior to analysis and then to redissolve it in a suitable solvent. Typical extraction procedures often produce extracts that generally contain a small amount of wax. Frequently, removal of such oligomers from an extract is necessary, e.g. by means of precipitation, centrifuging, precolumn filtration or protection (use of a reversed-phase guard column). In SEC separations the presence of polyolefin wax does not usually disturb provided that the MW of the wax is higher than that of the analysed compounds. 

Desorption chemical ionisation (DCI) mass spectrometry has been used for detecting additives extracted from polymers [51,52] by a solvent as volatile as possible. To use the DCI probe, 1 -2 iL of the sample, in solution, are applied to the probe tip, composed of a small platinum coil, and after the solvent has been allowed to evaporate at room temperature, the probe is inserted into the source. The sample is then subject to fast temperature ramping. DCI does not seem to be the most suitable mass-spectrometric method for analysis of dissolved polymer/additive matrices, because ... 

Gas chromatographic methods are used for the analysis of organic additives extracted from polymers with solvents and other liquid media or evolved by heating. 

Table 2.2 Solvent extraction methods of additive extraction from polymers ...

IR spectra obtained. LC-FTIR and SFC-FTIR microscopy have been used to identify additives extracted from polymer samples (cfr. Chps. 7.3.3.1 and 7.3.2.1 of ref. [77a]). 

Table 1.2 - Solvent Extraction Methods of Additive Extraction from Polymers... 

A number of antioxidants have been accepted by the FDA as indirect additives for polymers used in food appHcations. Acceptance is deterrnined by subchronic or chronic toxicity in more than one animal species and by the concentration expected in the diet, based on the amount of the additive extracted from the polymer by typical foods or solvents that simulate food in their extractive effects. Only materials of insignificant risk to the consumer are regulated by the FDA for use in plastics contacted by food stuffs. 

Applications The broad industrial analytical applicability of microwave heating was mentioned before (see Section 3.4.4.2). The chemical industry requires extractions of additives (antioxidants, colorants, and slip agents) from plastic resins or vulcanised products. So far there have been relatively few publications on microwave-assisted solvent extraction from polymers (Table 3.5). As may be seen from Tables 3.27 and 3.28, most MAE work has concerned polyolefins. 

A common technique used for polyolefin samples is to dissolve the sample using solvents such as xylene, decalin, toluene and di- or trichlorobenzene heated to temperatures as high as 130-150°C. After the plastic sample has been solvated, the polymeric component is precipitated by cooling and/or by adding a cold nonsolvent such as acetone, methanol or isopropanol. Polypropylene does not completely dissolve in toluene under reflux for 0.5 to 1 h with magnetic stirring (typically, 2g of polymer in 40 mL of toluene), yet the additives may be extracted [603]. In addition to additives, most solvents also extract some low-MW polymer with subsequent contamination of the extract. To overcome this a procedure for obtaining polymer-free additive extracts from PE, PP and PS has been described based on low-temperature extraction with n-hexane at 0°C [100],... 

An excellent and comprehensive review has covered HPLC analysis of AOs and light stabilisers up to 1990 [576]. Normal vs. reversed-phase and isocratic vs. gradient-elution HPLC separation of synthetic mixtures of additives and of solvent extracts from polymers were discussed. 

Methylene dichloride is a particularly good solvent for PP extraction because of its high volatility. In addition to additives, most solvents also extract some low molecular weight polymer with subsequent contamination of the extract. To overcome this, Slonaker and Sievers [2] have described a procedure for obtaining polymer-free additive extracts from PE based on low temperature extraction with n-hexane at 0 C. This procedure is also applicable to PP and PS. 

Mass spectrometry is used as a fingerprint technique to identify components of additive systems extracted from polymers [87, 88]. 

Polymer extraction procedures using organic solvents do not extract all types of organic additives from polymers, also many inorganic compoimds and metallo-organic compounds, (e.g., calcium stearate) are insoluble. The presence of metals will have been indicated in the preliminary examination of the polymer. Most types of organic polymer additives, however, can be readily extracted from polymers with organic solvents of various types. 

FIFA systems are highly flexible and may be interfaced to a variety of instruments ineluding UV-visible absorbance, pH, and redox detectors, and mass spectrometers (by the use of a particle beam interface, for example). Specific reaction chemistries can be accomplished through the use of dedicated in-line heaters and reaction coils. These types of systems can be used for the determination of the acid number of polymer solutions, additives content from polymer extracts, and trace analyses of other inorganic or organic components. 

Like other forms of molecular spectroscopy, MS may be used as a fingerprint technique to identify the components of additive systems extracted from polymer compositions. The strengths of MS are high sensitivity and the ability to distinguish between closely related compounds of differing relative molecular mass, e.g., the various alkyl thiodipropionates used as synergistic stabilisers in polyolefins and the UV-absorbing benzotriazole derivatives. 

For additives extracted from polyolefins, usually with diethyl ether, the extract is refluxed with ethanol and the solution is decanted from the insoluble residual polymer. On cooling, additives such as dilauryl and distearyl thiodipropionate separate out and are identified by infrmed examination. A 30 ul volume of the ethanolic solution is then spotted on to a thin Kieselgel 60 TLC plate and eluted with a suitable solvent, usually 98.5 + 1.5 toluene-ethyl acetate. The eluted plate is dried and sprayed with colour-developing reagents and the spots are examined. If the spots are to be submitted to mass spectrometric examination, methanolic iodine is used as the colour-developing reagent as this does not over-complicate the mass spectrometry. 

In addition, the intercept obtained by extrapolating this asymptote back to sin (0/2) = 0 equals (2M )". Note that both Mand are number averages when this asymptotic limit is used. This is illustrated schematically in Fig. 10.15 and indicates that even more information pertaining to polymer characterization can be extracted from an analysis of the curvature in Zimm plots. 

Starch is a polysaccharide found in many plant species. Com and potatoes are two common sources of industrial starch. The composition of starch varies somewhat in terms of the amount of branching of the polymer chains (11). Its principal use as a flocculant is in the Bayer process for extracting aluminum from bauxite ore. The digestion of bauxite in sodium hydroxide solution produces a suspension of finely divided iron minerals and siUcates, called red mud, in a highly alkaline Hquor. Starch is used to settle the red mud so that relatively pure alumina can be produced from the clarified Hquor. It has been largely replaced by acryHc acid and acrylamide-based (11,12) polymers, although a number of plants stiH add some starch in addition to synthetic polymers to reduce the level of residual suspended soHds in the Hquor. Starch [9005-25-8] can be modified with various reagents to produce semisynthetic polymers. The principal one of these is cationic starch, which is used as a retention aid in paper production as a component of a dual system (13,14) or a microparticle system (15). 

The Ts of methacryhc polymers may be regulated by the copolymerization of two or more monomers as illustrated in Figure 1. The approximate T value for the copolymer can be calculated from the weight fraction of each monomer type and the T (in K) of each homopolymer (15). Acrylates with low transition temperatures are frequently used as permanent plasticizers (qv) for methacrylates. Unlike plasticizer additives, once polymerized into the polymer chain, the acrylate cannot migrate, volatilize, or be extracted from the polymer. 

The aim of this chapter is to summarize some of the research findings on xylan, a natural polymer extracted from corn cobs, which presents a promising application in the development of colon-specific drug carriers. Physicochemical characterization of the polymer regarding particle size and morphology, composition, rheology, thermal behavior, and crystallinity will be provided. Additionally, research data on its extraction and the development of microparticles based on xylan and prepared by different methods will also be presented and discussed. 

Conventional extraction technologies. . 59 from polymer/additive ... 

Isolation of the products from complex matrixes (e.g. polymer and water, air, or soil) is often a demanding task. In the process of stability testing (10 days at 40 °C, 1 h at reflux temperature) of selected plastic additives (DEHA, DEHP and Irganox 1076) in EU aqueous simulants, the additive samples after exposure were simply extracted from the aqueous simulants with hexane [63]. A sonication step was necessary to ensure maximum extraction of control samples. Albertsson et al. developed several sample preparation techniques using headspace-GC-MS [64], LLE [65] and SPE [66-68]. A practical guide to LLE is available [3]. 

The efficacy and rate of the extraction process of additives from polymers are influenced by numerous factors including ... 

More recently, some novel pressurised procedures for extraction of additives from polymers have been developed (Table 3.3). The principal objectives of all these techniques, such as SEE [89], MAE [90] and pressurised fluid extraction (PEE), is to replace the conventional extraction methods by shortening the extraction time, reduction in solvent use and automation. 

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